Sialoglycoconjugates are cell surface components involved in many aspects of cellular response to extracellular changes and stimuli. Of all the biochemical changes associated with neoplasia, modifications of these components and their biosynthesis have been best documented. In order to monitor sialoglycoconjugates in the surface membrane of living cells with the fluorescence microscope and biochemical techniques, we plan to introduce a covalently bonded fluorescent label into the sialic acid moiety. This will be achieved by condensation of dansylhydrazine as fluorophor with the C7-sialic acid aldehyde produced by mild periodate oxidation. Preliminary data show the specificity of the procedure for sialic acids. The fluorophor will be made impenetrable to the membrane by a) complexing with cycloheptaamylose, incorporation into b) polystyrene beads or c) lipid micelles or, d) by synthesis of a hydrophilic, negatively charged derivative. The quantitative nature of the labeling will be evaluated by microspectrofluorometry as well as biochemical analysis. The dansylated products of proteolysis of whole cells and of their solubilized surface glycoproteins will be compared to determine their relationship. The procedure will be adapted for electron microscopy by tritium labeling, anti-dansyl-antibody techniques and heavy metal staining of a sulfonated dansylderivative. All the techniques developed will be used to study the mobility of sialoglycoconjugates in the cell surface in response to lectin binding. The technique will allow to monitor and separate cell populations on the basis of their surface sialic acid content and might therefore be useful in flow-microfluorometry as a tool for cancer diagnosis and research.